In recent years, active research has been conducted for the energy harvesting technology. The energy harvesting technology is for converting various types of energy widely present in the environment into electric power, and maintenance free is realized in supplying power.
As an example of the energy harvesting technology, there is known a vibration piezo generator for converting vibrations present in the living environment into electric power. There are vibration piezo generators of various structures, and a piezoelectric generator is known as one example. There are piezoelectric generators of various structures.
As one example of a piezoelectric generator, there is known a vibration piezo generator including a weight attached to the front end of a cantilever and a piezoelectric element provided on the cantilever formed by sequentially laminating a lower electrode, a piezoelectric film, and an upper electrode. Power generation of a vibration piezo generator is performed by deforming the piezoelectric film via the cantilever to which vibration is applied, so that a piezoelectric effect is generated in the piezoelectric film. PZT and AlN are known as examples of piezoelectric materials.
As an application target of such a vibration piezo generator, there is known a power supply source for a device in which vibration is generated, such as a power supply source for an acceleration sensor attached inside a tire of a vehicle. In this case, the vibration piezo generator is attached to the device in which vibration is generated, such as a device in a tire.
This kind of vibration piezo generator typically has an element size of approximately several hundreds of μm through several mm, and is generally fabricated by microscopic processing used for manufacturing MEMS (Micro Electro Mechanical System).
Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-116668
Patent Document 2: Japanese Laid-Open Patent Publication No. 2008-197140
Patent Document 3: Japanese Laid-Open Patent Publication No. 2005-186930
Non-Patent Document 1: Proceedings of the 14th International Conference on Solid-State Sensors, Actuators and Microsystems, Lyon, France, Jun. 10-14, 2007, p. 891-894
Non-Patent Document 2: IMEC Newsletter 54, October 2008, p. 1, 10
Non-Patent Document 3: T. Nishida, Univ. Florida et al. US Patent Application Publication, No. US 2004/0007942 (Jan. 15, 2004)
In a vibration piezo generator having a cantilever and a weight as described above, the resonance frequency is determined by the shape and the material of the cantilever and weight. Furthermore, in the vibration piezo generator, when the vibration frequency from outside and the resonance frequency match, a large amount of electric energy is generated. However, as the difference in these frequencies increases, the generated electric energy decreases.